On my BMW motorcycle (R1150R) there is a not original oil cap installed. It has 4 holes to open and was probably delivered with a suitable tool. Because I bought the machine used and the tool was not delivered with it, I have drawn a suitable key, printed it out and added 2 pcs. M3x8 stainless steel hexagon socket screws. This key is now included in the tool kit.
The files for the wrench are on Thingiverse: https://www.thingiverse.com/thing:4549882